bone cell growth. As such, a hydrophilic surface serves as a better
substrate for bone cell growth than a hydrophobic surface.

“An important aspect for osseointegration is the implant’swetting behavior, i.e., if it is hydrophilic or not,” said Brogren. “Agood wetting behavior of the implant will lead to a faster inte-gration of the implant. This effect is dependent upon how theimplant is handled, cleaned, and packaged.”Coatings can also be applied to facilitate implant hydrophilic-ity as well as independently stimulate bone growth. One suchcoating material that has become quite common to facilitate os-seointegration is the naturally occurring mineral form of calciumapatite called hydroxyapatite—or HA for short.

“Typically, porous coatings are requested, with absolute largeporosity (> 40 percent), large size pores (>200 um), with, at thesame time, good enough mechanical performances to guaranteeintegrity under the physiological cycling loads. On top, a changeof the chemical nature can be requested: for example, pass from aCoCr (cobalt chromium) bulk to a porous titanium surface, fromtitanium alloy to hydroxyapatite, etc.,” commented Robotti. “Themost interesting novelty comes in the new couplings, such as ti-tanium coating on PEEK, titanium coating on polyethylene, ortitanium coating on ZTA (zirconia toughened alumina). How-ever, these configurations need accurate TPS process control toguarantee solid results.”HA coatings have become particularly sought-after for or-thopedic applications largely because up to 50 percent of humanbone volume is composed of HA. The material is already usedas a filler to replace amputated bone and has found success inuse as a coating to promote bone ingrowth in prosthetic devices.Titanium coatings have traditionally been used because they arecapable of connecting structurally and functionally with bone,but HA is becoming increasingly popular due to its enhanced os-seointegrative capability as a result of bone material mimicry.

HAnano Surface, one such HA-based coating, was introduced
in the United States for the orthopedic market in 2016. Just 20
nanometers thin and applicable to a wide variety of implant materials, HAnano has demonstrated increased anchoring strength
and integration with surrounding bone tissue.

“What we also know is that a coating
such as HAnano Surface does not only
improve the hydrophilicity initially, but
that this effect is stable over time,” stated
Brogren. “Thus, by choosing an appropriate coating, the wetting behavior will be
enhanced also after storing of the product.
Because of the increased focus on osseointegration in orthopedics, a hot topic for
the coming years will be how to improve
hydrophilicity of implants, and how to
maintain this effect on the implant—from
manufacturing until placed into the patient.
Surface modifications and coatings can play
an important role in this; we have shown
that HAnano Surface maintains a hydrophilic implant surface over a long time.”

Covering All the Bases

Suppliers and OEMs alike have come to
somewhat of a consensus that additive
manufacturing (AM) is the way of the future for orthopedic devices. That technological approach also enables specific surface design—3D-printed titanium could
have its porous structure, shape-morphol-